I. Technical Field
The present invention pertains generally to telecommunications, and particularly to a High Speed Downlink Packet Access (HSDPA) system such as that operated (for example) in a Universal Mobile Telecommunications System (UMTS) terrestrial radio access network (UTRAN).
II. Related Art and Other Considerations
In a typical cellular radio system, mobile terminals (also known as mobile stations and mobile user equipment units (UEs)) communicate via a radio access network (RAN) to one or more core networks. The user equipment units (UEs) can be mobile stations such as mobile telephones (“cellular” telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by a unique identity, which is broadcast in the cell. The base stations communicate over the air interface (e.g., radio frequencies) with the user equipment units (UE) within range of the base stations. In the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology.
As wireless Internet services have become popular, various services require higher data rates and higher capacity. Although UMTS has been designed to support multi-media wireless services, the maximum data rate is not enough to satisfy the required quality of services.
In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity. One result of the forum's work is the High Speed Downlink Packet Access (HSPA). The High Speed Packet Access (HSPA) enhances the WCDMA specification with High Sped Downlink Packet Access (HSDPA) in the downlink and Enhanced Dedicated Channel (E-DCH) in the uplink. These new channels are designed to support IP based communication efficiently, providing enhanced end-user performance and increased system capacity. Though originally designed for interactive and background applications, they provide as good or even better performance for conversational services than the existing CS bearers.
Concerning High Speed Downlink Packet Access (HSDPA) generally, see, e.g., 3GPP TS 25.435 V6.2.0 (2005 June), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; UTRAN Iub Interface User Plane Protocols for Common Transport Channel Data Streams (Release 6), which discusses High Speed Downlink Packet Access (HSDPA) and which is incorporated herein by reference in its entirety. Also incorporated by reference herein as being produced by the forum and having some bearing on High Speed Downlink Packet Access (HSDPA) or concepts described herein include: 3GPP TS 25.425 V6.2.0 (2005 June), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; UTRAN Iur interface user plane protocols for Common Transport Channel data streams (Release 6); and 3GPP TS 25.433 V6.6.0 (2005 June), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; UTRAN Iub interface Node B Application Part (NBAP) signaling (Release 6).
High Speed Downlink Packet Access (HSDPA) is also discussed in one or more of the following (all of which are incorporated by reference herein in their entirety):
U.S. patent application Ser. No. 11/024,942, filed Dec. 30, 2004, entitled “FLOW CONTROL AT CELL CHANGE FOR HIGH-SPEED DOWNLINK PACKET ACCESS”;
U.S. patent application Ser. No. 10/371,199, filed Feb. 24, 2003, entitled “RADIO RESOURCE MANAGEMENT FOR A HIGH SPEED SHARED CHANNEL”;
U.S. patent application Ser. No. 11/292,304, filed Dec. 2, 2005, entitled “Flow Control For Low Bitrate Users On High-Speed Downlink”;
PCT Patent Application PCT/SE2005/001247, filed Aug. 26, 2005; and
PCT Patent Application PCT/SE2005/001248, filed Aug. 26, 2005.
HSDPA achieves higher data speeds by shifting some of the radio resource coordination and management responsibilities to the base station from the radio network controller. Those responsibilities include one or more of the following (each briefly described below): shared channel transmission, higher order modulation, link adaptation, radio channel dependent scheduling, and hybrid-ARQ with soft combining.
In shared channel transmission, radio resources, like spreading code space and transmission power in the case of CDMA-based transmission, are shared between users using time multiplexing. A high speed-downlink shared channel is one example of shared channel transmission. One significant benefit of shared channel transmission is more efficient utilization of available code resources as compared to dedicated channels. Higher data rates may also be attained using higher order modulation, which is more bandwidth efficient than lower order modulation, when channel conditions are favorable.
The radio base station monitors for the channel quality (CQ) of the high-speed downlink shared channel (HS-DSCH) and manages a priority queue maintained at the radio base station. The base station's priority queue (PQ) stores data which is to be sent on the high-speed downlink shared channel (HS-DSCH) over the air interface to the mobile terminal. In addition, knowing from the monitor the carrier quality of the HS-DSCH, the base station sends to the control node messages which authorize the control node to send more HS-DSCH data frames to the radio base station.
The mobile terminal reports a channel quality indicator (CQI) to the radio base station in charge of the cell. The CQI is a measure of the quality of the common pilot CPICH as reported by each mobile station (e.g., each user equipment unit (“UE”)). The channel quality indicator (CQI), together with an expression(s) of capabilities of the mobile terminal, is translated to a bitrate. The bitrate is then further reduced if needed by the radio base station, which results in generation of capacity allocation control frames which are sent to the control node regularly and/or per need bases, e.g. at urgent transitions. The authorizing messages include a “capacity allocation” which can be expressed in various ways, such as in terms of either bitrate or credits, for example. For example, capacity allocation expressed in credits may refer to a number of MAC-d PDUs that the radio network controller (RNC) is allowed to transmit for the MAC-d flow. In response to these authorizing messages, the control node sends further HS-DSCH frames to the radio base station.
The data in the priority queues is sent from a control node to a radio base station in protocol data units (PDUs). A number of PDUs may be included in each high-speed downlink shared channel (HS-DSCH) data frame.
Thus, HSDPA is a shared channel designed for efficient support of packet data applications. Enhancements over dedicated (and shared) channels include fast link adaptation; fast scheduling; Hybrid ARQ from Node B; and a short transmission time interval (TTI). In terms of fast link adaptation, the link adaptation is done by selecting the best modulation and coding scheme based on channel quality indicator from the UE. For fast scheduling, the selection of the user is done in the Node B, which has access to the link quality information, and thus can select the optimal user. Hybrid ARQ from Node B involves having a retransmission mechanism in the base station which allows fast retransmissions and quick recovery of erroneous link adaptation decisions. As a short TTI, a two millisecond (ms) TTI is used for all transmissions.
E-DCH is a dedicated channel that has been enhanced for IP transmission. Enhancements include the possibility of using use a shorter TTI; fast hybrid ARQ (HARQ) between mobile terminal and the base station; scheduling of the transmission rates of mobile terminals from the base station; and the fact that E-DCH retains majority of the features characteristic for dedicated channels in the uplink. In terms of fast hybrid ARQ (HARQ) between mobile terminal and the base station, the HARQ mechanism is semi-persistent, as it will abandon a transmission after a fixed number of transmission attempts. The number of transmission attempts is signaled from the RNC to the UE.
Base stations provided with high-speed downlink packet access capability typically have a high-speed downlink packet access controller, e.g., a HSDPA scheduler or similar channel manager that governs allocation and utilization of the high-speed downlink shared channel (HS-DSCH) and a high-speed shared control channel (HS-SCCH) which is utilized for signaling purposes. The HSDPA controller is commonly referred to also as HSDPA scheduler. The HS-SCCH contains information which is sent to the mobile terminals so that the mobile terminals know if they have data to receive on the HS-PDSCh channel or not. The high-speed downlink shared channel (HS-DSCH) and the high-speed shared control channel (HS-SCCH) are separate channels. As understood by those skilled in the art, the signaling carried by the high-speed shared control channel (HS-SCCH) is performed by transmitting the HS-SCCH TTI two slots in advance of the corresponding HS-DSCH TTI.
One example HSDPA scheduler executes an algorithm for determining scheduling priority for each user, e.g., each user equipment unit (UE). The scheduling priority algorithm receives two primary inputs. Separate priority factors for the scheduling priority algorithm are computed for each of these two primary inputs, and are multiplied together.
A first input to the scheduling priority algorithm is related to a time delay for a packet; the second input is related to a channel quality index (CQI).
The first input to the scheduling priority algorithm is the time delay parameter for a packet residing in a transmission buffer of the base station node and destined for the user equipment unit (UE). This first input results in a priority delay factor, which is computed by passing the time remaining until the packet is too old to a barrier function. For example, the delay factor can be computed as 1/timeLeft (“timeLeft” being the time left in the buffer), with a maximum delay factor of 100 being permitted, which results in the curve of FIG. 1A. As shown in FIG. 1A, when time left, i.e. when the remaining time before the packet is dropped is 50 ms the delay factor is 20.
This time delay parameter can be related to or a function of several other parameters, and preferably four parameters a, b, t1, and t2. FIG. 1B shows a parameterized function for the time delay parameter, and illustrates that parameters t1 and t2 are limits on the time left scale (i.e., describing when to change the slope of the curve), and parameters a and b are parameters that define the slope for the first part of the barrier function. Therefore, the delay factor is computed as a function of the timeLeft, i.e timeleft=Threshold−TimelnQueue, as described by Expression 1:
      f    ⁡          (      timeLeft      )        =      {                                        -                          b              ⁡                              (                                  timeLeft                  -                                      t                    1                                                  )                                                                                        for              ⁢                                                          ⁢              timeLeft                        <                          t              1                                                                                                                        (                                      timeLeft                    -                                          t                      2                                                        )                                2                            ⁢                                                a                  -                  1                                                                      (                                                                  t                        1                                            -                                              t                        2                                                              )                                    2                                                      +            1                                                              for              ⁢                                                          ⁢                              t                1                                      ≤            timeLeft            <                          t              2                                                            1                                                    for              ⁢                                                          ⁢                              t                2                                      ≤            timeLeft                              
When the packet is delayed up to a delay threshold time (dth), the packet is discarded. The delay based priority function is illustrated in FIG. 1B.
The second input to the scheduling priority algorithm is related to a channel quality index (CQI), i.e. the measured and reported CQI, or simply the Carrier to Interference Ratio (CIR). The channel quality index (CQI) priority factor is the current reported CQI divided with low pass filtered previous reported CQI or simply average CQI.
For a successful cellular service, a number of considerations are involved. One such consideration is area coverage, e.g., geographical coverage. Of concern in service provision and network design is the fact that a user equipment unit (UE) may suffer from degrading radio coverage, particularly near a cell border or coverage “hole” within a cell.
What is needed therefore, and an object of the present invention, are apparatus, methods, and techniques for enhancing cellular service, and in particular HSDPA coverage, in a telecommunications system.